This is a performance analysis and review article of the SONY FE 35mm F1.4 GM.
You hardly understand the specific differences in how the lenses work and how their performance differs from each other, do you?
Even if you look it up in magazines or on the Internet, all you will find are similar "word-of-mouth recommendations" and articles like that.
In this blog, while researching the history of lenses and their historical background, we estimate lens design performance based on patent information and actual shooting examples, and analyze lens performance in detail from a technical viewpoint through simulations.
Professional lens designer Jin Takayama will carefully unravel optical characteristics such as optical path diagrams and aberrations, which are generally not visible, and explain the taste and descriptive performance of lenses in a deep and gentle manner.
Now, please enjoy the special information that you can read only on this blog in the world.
The SONY FE 35 mm f / 1.4 gm is a large-aperture, wide-angle, single-focus lens bearing the designation "G Master" for the high-performance lens for Sony's mirrorless single-lens FE mount.
As you know, SONY FE lenses are divided into 4 grades.
- ZEISS (ZA,Z)
- G Master (GM)
The G grade was originally a title given to MINOLTA's high-grade lenses, but SONY, which inherited MINOLTA's camera operations, established the "G Matser" grade, which is even higher than the G, and gave the name only to ultra-high-performance lenses.
Next, let's look back on the lineage of 35 mm f / 1.4 specification lenses from MINOLTA to SONY.
First of all, it seems that the 35 mm large-diameter SLR lens of MINOLTA started with the F1.8, but the F1.4 large-diameter lens will be released about two years after the birth of the world's first autofocus single-lens alpha system.
After that, the camera business was sold from MINOLTA to SONY, and now (2021) there are two F1.4 lenses, which are arranged in order of the year of release.
- 1987 MINOLTA AF 35mm F1.4
- 2006 SONY SAL35mm F1.4G (MINOLTA)
- 2015 SONY Distagon T * FE 35 mm F1.4 ZA
- 2021 SONY 35mm F1.4 GM(this article)
In the previous analysis, we analyzed the (3) SONY FE 35 mm F1.4 ZA, which has undergone a full renewal for the first time in about 30 years, and were impressed by the improved performance of the threat.
This (4) SONY FE 35 mm f / 1.4 gm introduced in this article is about 6 years after the ZISS version, so it is a little early for a successor.
In addition to the 35 mm f / 1.4 specification, which can be said to be the representative of each company's lens series in recent years, the performance of this lens, which is given the inscription "GM" as a symbol of the prestige of SONY lens, is expected to increase.
Because SLR cameras with mirrors must have a long back focus, the shorter the focal length of the wide-angle lens, the more difficult it is to design. And the 35 mm focal length is just the first lens that becomes difficult to design.
I think I have made such an explanation from time to time in the past, but I will explain the reason for this a little by illustrating it using a simulation.
First, organize the definitions of back focus and flange back.
- Flange back: a distance from a coupling surface (mounting surface) of the lens and the camera to the image pickup element;
- Back focus: the distance from the side of the imaging element of the lens to the imaging element
At the top of the above diagram is a NIKKOR 35 mm F2.0D that we have analyzed in the past.
The lower row shows an optical system consisting of a single lens with a focal length of 35 mm (hereinafter referred to as a single optical system).
Compared to the NIKKOR 35 mm, you can see that the back focus of the single-lens optical system is shorter.
Since the back focus of the single-lens optical system is slightly smaller than the focal length, the back focus of this single-lens optical system is approximately 32 mm for a focal length of 35 mm.
By contrast, the NIKKOR 35 mm has a back focus of about 36 mm, which is longer than the focal length (35 mm).
A single-lens reflex camera requires a back focus of about 36 mm because a mirror is placed between the lens and the image pickup device to direct light to the viewfinder, and a shutter is placed to control the exposure time.
- The minimum required back focus varies slightly depending on the manufacturer.
Roughly speaking, the focal length is the "length of the optical system", so it is natural that the focal length and the back focus are proportional.
To put it simply, for a wide-angle lens with a short focal length, it is natural that the back focus is also short.
However, with a wide-angle lens with a short focal length, you can't use it for a single-lens reflex camera if the back focus is also short.
This requires an "unnatural optical design" where the focal length is short but the back focus is long.
As a result, design freedom is limited, and wide-angle lenses tend to be more difficult to design.
Therefore, how to design a large aperture lens with a focal length of 35 mm has become a "battlefield" in terms of all the technologies of each company.
In addition, if the focal length is 50 mm, the back focus will be sufficiently long and there will be a margin.
The figure below shows an optical system with a focal length of 28 mm, 35 mm, or 50 mm made up of a single lens.
As shown in the figure above, the back focus becomes longer in proportion to the focal length. From a focal length of 50 mm or so, a margin of the back focus, where mirrors and shutters are placed, is automatically secured, making it easier to design.
That's why mirrorless single-lens cameras are attracting attention. As the name suggests, this camera has no mirror, so there is no problem with a short back focus. The problem of "unnatural optical design" with wide-angle lenses is solved, and miniaturization and ultra-high performance are expected.
Now, let's take a look at the analysis data to see how effective it was.
A search of the patent literature shows that WO2020/213337 describes embodiments of multiple types of lens specifications.
Although the embodiment from the ultra-wide angle lens to the focal length of 35 mm was described, the embodiment 6 has the same specification as the focal length of 35 mm f / 1.4 and this product, and the composition is not exactly the same, but it seems to be quite similar.
The following design values have been selected and reproduced from the appropriate patent literature and do not correspond to the actual product. Naturally, the data is not guaranteed, and I am not responsible for any accidents or damages that may occur by using this data.
Analysis of Design Values
Optical Path Diagram
Above is the optical path diagram similar to SONY FE 35 mm f / 1.4 gm.
It consists of 12 groups and 15 lenses, and adopts an aspherical lens for the first lens on the most object side and the 14th lens on the second side from the image sensor side.
The real SONY FE 35 mm f / 1.4 gm has 14 lenses in 10 groups, which is one less, and the composition of the cemented lens is slightly different, but the arrangement of the aspherical lens and the composition of the focusing lens are similar, so it seems that they are the same in terms of design philosophy.
The performance of the actual product may have been brushed up.
Graphs of spherical aberration, image surface curvature, and distortion
If you look at the spherical aberration, it's very small to make you think it's some kind of joke. In particular, you can't help but marvel at the way the color components come together toward the top of the graph.
Considering the 35 mm f / 1.4 spec, the axial chromatic aberration is also in an amazing compensation state.
I am afraid that this level of aberration correction can be realized in a product with a practically unbreakable size.
The field curvature has multiple undulations, but it is small in absolute terms.
IF I SELL THE SOUL TO THE DEVIL, I WONDER IF I CAN CORRECT IT LIKE THIS.
Distortion aberration is corrected to a value close to zero even though it is almost the specification of a wide-angle lens.
Distortion can be reduced by image processing, so in recent years there have been some manufacturers that allow distortion to be reduced to zero as an optical system. Does this mean that you are showing the spirit of being the top mirrorless manufacturer?
Although it can be reduced by image processing, it is true that there are concerns that noise will increase or the angle of view will change by processing, so it is better to be corrected as an aberration.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
The lateral chromatic aberrations is not large in absolute values, but the C line (red) seems to stand out a little and I am concerned about it. However, I think it will be automatically corrected by image processing, so I don't think there is anything to worry about practically.
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as Transverse Aberrations.
It can be seen that the amount of aberration at the d-line (yellow), which is the reference ray, is extremely small. However, there seems to be some bending of the g-line (blue) and F-line (light blue) from around the image height of 18 mm or more in the peripheral area of the screen in the tangential direction, which is related to the fact that there is still some lateral chromatic aberrations.
That said, the other aberrations are so small that it just bothers you, which is a luxurious point to make.
Spot Scale 0.3 (Standard)
This is the result of an optical simulation, but first let's look at the spot diagram.
Because it is such a beautiful lateral aberration chart, it is almost dotted in the whole area.
Spot Scale 0.1 (Detail)
Maximum Aperture F1.4
Finally, let's look at the results of the MTF simulation.
High! Amazing height from release.
Small Aperture F4.0
The ONY FE 35 mm F1.4 GM was born as the face of the E mount system, so it is obvious that it is an incredibly high-performance lens.
However, the information discovered this time is slightly different in composition from the actual product lens, and there is a possibility that it hides the unbelievable fact that there is a high possibility that the actual product has been brushed up further.
In the end, I'd like to check the actual picture as soon as possible.
Example photos are in preparation.
If you are looking for analysis information on other lenses, please refer to the table of contents page here.